The proposed study will objectify the sleep physiology of surgical in-patients with varying degrees of illness. Four groups of surgical patients will be investigated, each representing an increasing level of trauma: herniorrhaphy, cholecystectomy, and gastrectomy patients and those patients ill enough to require placement in an intensive care unit (ICU). For the first three groups all night sleep data will be gathered preoperatively and on consecutive post-operative nights until sleep is restabilized. ICU patients will be studied for up to fourteen consecutive nights in the unit. EEG, EOG, EMG, EKG, and respiratory rate will be recorded on a polygraph, hand scored, and treated and stored by computer. For each patient night a sleep schedule -- an analogue record of sleep stage sequence in time -- and a table of relevant sleep parameters will be maintained. Patterns of sleep physiology will be defined in response to the trauma and during recovery within and across the various patient groups. In the first of the surgical groups the effects of meperidine will be studied so as to define its contribution to altered sleep patterns. In the study of ICU patients clinical events will be recorded and related to the sleep stage in which they occur and to the aberrations of sleep in this particular group. The purpose here is to define how quality of sleep may bear on critical events in illness and relate to the course of recovery. An effort will be made, too, to perfect an electronic method for scoring sleep stage. We have also successfully developed and will continue to emphasize interdisciplinary cooperation whereby there is an effective interdigitation between researchers and surgical and nursing personnel.